The present invention relates to a snap-in coupling for releasably connecting a first structural member and a second structural member.
DE 198 36 108 A1 discloses a snap-in coupling comprising an elastically deformable female coupling member and a male coupling member. The female coupling member is adapted to be inserted into a socket provided at said first structural member so as to be positively retained therein. It comprises a spherical female portion, an annular intermediate wall integral therewith and serving as an insertion portion, and a tubular outer wall integral with said intermediate wall, which outer wall engages a peripheral wall of the socket when the female coupling portion is inserted into the socket. The male coupling member comprises a head portion and a mounting portion adapted to be fixed to the second structural member.
In this prior snap-in coupling the intermediate wall of the female coupling member is of conical shape and is stiffened by webs which extend between the tubular outer wall of the female coupling member and which are connected to the outside of the spherical female portion by radial ribs. The female coupling member is made of thermoplastic elastomeric material or rubber. This snap-in coupling has vibration dampening characteristics due to its geometry and the used material so that it provides for vibration decoupling between the first and second structural members.
German Utility Model 202 16 836 discloses a snap-in coupling wherein the annular intermediate wall of the female coupling member is not of conical shape but of an undulated or corrugated profile. This provides for resiliency not only in axial directions but also in radial directions. Therefore the female coupling member may perform vibration decoupling compensation movements both in axial and radial directions and, accordingly, in all directions therebetween, i.e. three-dimensional compensation movements in space.
This allows to make the female coupling member of relatively hard plastic material, for example an elastomeric material on the basis of chemically and thermally deformation resistant polyester. For example polybutylenetherephthalate (PBT) and polyethylenetherephthalate (PET) may be used.
These materials are of temperature dependent hardness. For example, when they are subject to extremely low temperatures down to −40° C. to be encountered in cold climatic zones they will become so hard that the snap-in coupling cannot be released by acceptable forces. Apart from the fact that the mounting and releasing forces are dependent on temperature it is relatively difficult to precisely set the absolute values of the mounting and, respectively, releasing forces for normal environmental conditions because the characteristics of the used plastic material as well as the geometry of the plastic female coupling member cannot be readily controlled.